• An artist's rendering of the asteroid Apophis.

    Image: European Space Agency

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  • Graphic: Christine Daniloff (original image: NASA)

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Paintballs may deflect an incoming asteroid

With 20 years’ notice, paint pellets could cause an asteroid to veer off course.

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Sarah McDonnell
Email: s_mcd@mit.edu
Phone: 617-253-8923
MIT News Office

In the event that a giant asteroid is headed toward Earth, you’d better hope that it’s blindingly white. A pale asteroid would reflect sunlight — and over time, this bouncing of photons off its surface could create enough of a force to push the asteroid off its course.

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How might one encourage such a deflection? The answer, according to an MIT graduate student: with a volley or two of space-launched paintballs.

Sung Wook Paek, a graduate student in MIT’s Department of Aeronautics and Astronautics, says if timed just right, pellets full of paint powder, launched in two rounds from a spacecraft at relatively close distance, would cover the front and back of an asteroid, more than doubling its reflectivity, or albedo. The initial force from the pellets would bump an asteroid off course; over time, the sun’s photons would deflect the asteroid even more.

Paek’s paper detailing this unconventional strategy won the 2012 Move an Asteroid Technical Paper Competition, sponsored by the United Nations’ Space Generation Advisory Council, which solicits creative solutions to space-related problems from students and young professionals. Paek presented his paper this month at the International Astronautical Congress in Naples, Italy.

The challenge put forth by this year’s U.N. competition was to identify novel solutions for safely deflecting a near-Earth object, such as an asteroid. Scientists have proposed a wide variety of methods to avoid an asteroid collision. Some proposals launch a projectile or spacecraft to collide with an incoming asteroid; the European Space Agency is currently investigating such a mission.

Other methods have included detonating a nuclear bomb near an asteroid or equipping spacecraft as “gravity tractors,” using a craft’s gravitational field to pull an asteroid off its path.

Paek’s paintball strategy builds on a solution submitted by last year’s competition winner, who proposed deflecting an asteroid with a cloud of solid pellets. Paek came up with a similar proposal, adding paint to the pellets to take advantage of solar radiation pressure — the force exerted on objects by the sun’s photons. Researchers have observed that pressure from sunlight can alter the orbits of geosynchronous satellites, while others have proposed equipping spacecraft with sails to catch solar radiation, much like a sailboat catches wind.

In his proposal, Paek used the asteroid Apophis as a theoretical test case. According to astronomical observations, this 27-gigaton rock may come close to Earth in 2029, and then again in 2036. Paek determined that five tons of paint would be required to cover the massive asteroid, which has a diameter of 1,480 feet. He used the asteroid’s period of rotation to determine the timing of pellets, launching a first round to cover the front of the asteroid, and firing a second round once the asteroid’s backside is exposed. As the pellets hit the asteroid’s surface, they would burst apart, splattering the space rock with a fine, five-micrometer-layer of paint.

From his calculations, Paek estimates that it would take up to 20 years for the cumulative effect of solar radiation pressure to successfully pull the asteroid off its Earthbound trajectory. He says launching pellets with traditional rockets may not be an ideal option, as the violent takeoff may rupture the payload. Instead, he envisions paintballs may be made in space, in ports such as the International Space Station, where a spacecraft could then pick up a couple of rounds of pellets to deliver to the asteroid.

Paek adds that paint isn’t the only substance that such pellets might hold. For instance, the capsules could be filled with aerosols that, when fired at an asteroid, “impart air drag on the incoming asteroid to slow it down,” Paek says. “Or you could just paint the asteroid so you can track it more easily with telescopes on Earth. So there are other uses for this method.”

Lindley Johnson, program manager for NASA’s Near Earth Objects Observation Program, says Paek’s proposal is “an innovative variation” on a method used by others to capitalize on solar radiation pressure. For example, MESSENGER, a spacecraft orbiting Mercury, is equipped with solar sails that propel the craft with solar radiation pressure, reducing the fuel needed to power it.

“It is very important that we develop and test a few deflection techniques sufficiently so that we know we have a viable ‘toolbox’ of deflection capabilities to implement when we inevitably discover an asteroid on an impact trajectory,” Johnson says.

William Ailor, principal engineer for Aerospace Corp. in El Segundo, Calif., adds that the potential for an asteroid collision is a long-term challenge for scientists and engineers.

“These types of analyses are really timely because this is a problem we’ll have basically forever,” Ailor says. “It’s nice that we’re getting young people thinking about it in detail, and I really applaud that.”

Topics: Aeronautical and astronautical engineering, Asteroids, Astronomy, Contests and academic competitions, Graduate, postdoctoral, NASA, Near-Earth objects, Research, Solar wind, Students


very interesting and innovative idea,which thus must be developed in order to be more reliable and realistic. The only problem is that solar radiation deflection process needs that much time to be efficient.Yet i think this woudn't constitute an obstacle in front of such brilliant young minds...
The mass of Apophis is about 27x10^9 kg, or about 27 megatons (not 27 gigatons).
Placing spacecraft in the vicinity of such an asteroid, each with a very large light reflecting panel (hundreds of square miles in area) could reflect and focus much more light on a painted asteroid thereby increasing/amplifying the light pressure force. In addition, the direction of the applied force could be more precisely controlled (i.e., orthogonal to the orbital path) which would 'push' an asteroid in an optimal direction vs. a radial force applied solely along the sun-asteroid direction. An alternative might be to use ground-based or moon-based high-powered lasers to add to the light pressure. I believe this technique has been proposed in the past for light sail spacecraft propulsion, but it would probably be helpful in the asteroid scenario as well.
Pardon Me for commenting, but if the shape of asteroid is not spherical will this work? if after first shot of paint there is wobble and it breaks in to two then what? to Push, the NEO Quad Jet Rocket Used to Deliver pay load at Mars will be much efficient. Thank you
ya its been a nice idea by the winner i just had a great doubt that if that solar radiation pressure can deviate the asteroid it takes about 20 years for a cumulative effect, then our earth and moon born about 4.54 billion years ago so as moon is of good reflector to the suns light so how much do think the moon has deflected, i think is is so much of deflection as it has passed 4.5 billion years. lets not think about moon or the earth ,just see the nearest planet to the sun (mercury) as it is near i will be having a high solar radiation pressure so think about how much its been deviated in these 4.54 billion years.
At risk of being considered a lunatic, I'd like to interject a related notion I've explored for many years. Instead of deflecting asteroids with white dust (TiO2), I think the dust could be used to encode useful information on the surface of our near neighbor, the moon. When I read of Mr. Paek's idea it occurred to me that the engineering challenges are similar. Astral catastrophe seems to lie inevitably in our planet's path. My hope is that this useful information on the surface of the moon might jump start our primitive progeny in the far flung future. This idea was formed as a result of a technical failure at a titanium dioxide factory over a quarter century ago. More details and photos can be found at RebelTao.com - Thank you for your consideration. Jimmy Tucker
The magnitude of impact of Apophis will be equivalent to 65000 times the Hiroshima bomb, can cause a Tsunami of 800-ft. see http://www.popularmechanics.com/science/space/deep/4201569 So it is necessary to have details of research of that MIT graduate, before reaching any conclusion, about his way of protecting the Earth by paintballs.
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